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Distance function from x to the Cantor set

  1. Sep 18, 2008 #1
    Does the said function satisfy:

    (2)never constant
    (3)has uncountably many zeroes

    1 and 3 is trivial, but I'm not sure about 2.
  2. jcsd
  3. Sep 22, 2008 #2
    Hello hello
  4. Sep 22, 2008 #3


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    I'm not sure how you'd even define the distance, given that every point in (0, 1) has a point in the Cantor set within epsilon for any epsilon > 0.
  5. Sep 22, 2008 #4
    Not true. The Cantor set is not dense in (0, 1). For example the point 1/2 is at least 1/6 away from any point in the Cantor (middle-thirds) set. In fact, dist({1/2}, CantorSet} = 1/6.
  6. Sep 23, 2008 #5


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    Ah... clearly I was thinking of something else. That'll teach me to post late at night!
  7. Sep 23, 2008 #6
    If x=1/2, then the distance from x to the Cantor middle-third set would be 1/6. If x=0, then the distance would be 0. Hence "not constant".

    I find the the use of the word "never" strange since it sounds to be like asserting otherwise the function would be constant on, say, the Tuesdays after a new moon, but not constant all other days.

    Possibly what you mean is that there are no open sets on which the function is constant.
  8. Sep 24, 2008 #7
    By "never" I mean that there is no interval on which it is constant.

    This is was a problem I thought up. My intuition was that since if a function is "continuous", and "never constant", each time you hit a zero you must "wave" up and down in order to hit a zero again. So this will make the number of zeros "countable". But the distance function from x to the cantor set seems to be "continuous and never constant" but has uncountably many zeros.
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